Natural gas provides a cost efficient and environmentally friendly alternative to gasoline as a fuel for combustion engines, particularly in motor vehicles. Thousands of motor vehicles have already been successfully converted to utilize natural gas as a fuel source instead of, or as an alternative to, gasoline. However, the use of natural gas as a fuel in motor vehicles present problems which are not encountered in gasoline powered motor vehicles.
Many of these problems arise because at environmental temperatures gasoline is a liquid, while natural gas, which consists primarily of methane, is gaseous. Thus, natural gas must be stored under high pressure in fuel cylinders specifically designed for motor vehicle use.
This gives rise to a number of requirements, most of which are safety-related:
1. It is essential that the high pressure gas be contained within the cylinder when the vehicle engine is not running. Over time, even minor leakage from the cylinder, particularly in an enclosed space such as a garage, can pose a considerable explosion hazard. PA1 2. The flow of gas into and out of the cylinder must be carefully controlled. Unlike a typical gasoline tank, which has a separate inlet and outlet, to minimize the potential for leakage a natural gas cylinder should preferably have only a single opening acting as both inlet and outlet. Cost considerations, particularly as an inducement to conversion from gasoline to natural gas usage, render it advantageous to utilize a single valve to control the flow of gas both into and out of the cylinder. However, a valve which is capable of permitting a controlled flow of gas out of the cylinder, under the high pressure conditions within the cylinder, must also be capable of withstanding the extremely high pressure reverse flow conditions that arise when gas is injected into the cylinder during filling. Known bidirectional valve designs are unsuitable for this application because the extremely high rate of gas flow through the cylinder opening, especially in filling but also in use, tends to cause sudden dislodgement of the sealing means (usually a gasket) used in such valves. PA1 3. Because of the nature of motor vehicles and their intended use, provision must be made to ensure that in case of collision the flow of gas out of the cylinder is immediately and completely interrupted. Furthermore, where means are provided for permitting the alternate use of natural gas and gasoline (or another fuel) in a motor vehicle engine, it is necessary to ensure that there is no flow of natural gas out of the cylinder when the engine is operating on gasoline or any other alternate fuel source.
In conventional natural gas vehicles there has been provided a solenoid valve or like means, and a check valve, each permitting only unidirectional gas flow. A solenoid valve provided at the inlet to the engine regulator controls the flow of gas from the cylinder into the engine. A check valve provided in a filling receptacle permits only the injection of gas into the cylinder. Although high standards must be maintained in order to ensure safety, the design of each check valve can be relatively simple because only a unidirectional flow of gas is required. The provision of both valves adds to both the cost of both installing original equipment and installing a conversion kit into a gasoline powered vehicle, and the cost of the equipment or conversion kit itself, and requires that many conduits and components outside of the cylinder be continuously under the high pressure conditions that exist within the cylinder.
For example, known natural gas vehicle cylinder valves utilize a manually operated screw thread actuator to control the flow of gas into and out of the cylinder for servicing or in case of an emergency. Manual valves tend to be kept open to permit easy refuelling and operation of the vehicle, with the result that the entire gas fuel system branching from the cylinder opening to the fuel lockoff solenoid valve at the regulator inlet, and to the filling receptacle, is continuously exposed to cylinder pressure. The potential for leakage, particularly in case of collision, can be significantly reduced by regulating the flow of gas at, or preferably inside, the cylinder opening.
The present invention overcomes these disadvantages by providing a cylinder fitting having a bidirectional solenoid valve fitted directly to the opening in the cylinder. The solenoid valve is adapted to both permit the injection of gas into the cylinder during filling and regulate the flow of gas out of the cylinder during operation of the vehicle.
In one embodiment of the cylinder fitting the solenoid valve is externally mounted. The cylinder fitting is adapted to be retrofitted to existing natural gas cylinders, and will replace (or render redundant) the fuel lockoff solenoid valve at the regulator inlet and the manual valve at the cylinder opening.
In a further embodiment of the cylinder fitting the solenoid valve is mounted inside the cylinder, thus protecting the valve from breakage and failure in case of a collision. The solenoid coil is contained within a low pressure chamber formed inside the cylinder by the cylinder fitting, effectively isolating the electrical components of the solenoid valve from the combustible gas within the cylinder and thereby permitting easy access for power supply lines.
These and other advantages will be apparent in the description of the present invention which follows.